Impact absorbing mechanism of walking robot

ABSTRACT

An impact absorbing mechanism, provided to a foot  5  of an extremity of each of two movable legs  2  of a bipedal walking robot  1  having the two movable legs  2 , includes: an upper base plate  5 - a  joined to a foot joint  4  of each of the movable legs  2 ; a lower base plate  5   b  positioned below the upper base plate, and being opposite to the upper base plate; and three elastic members  6  anisotropic in terms of elasticity, which are arranged at equal intervals in the circumferential direction about the yaw axis YA extending in a direction perpendicular to the upper base plate  5   a , between the upper base plate  5   a  and the lower base plate  5   b , each of which allows the lower base plate  5   b  to make elastic displacement relative to the upper base plate  5   a  in the same direction as axis YA extends, while each of which inhibits the lower base plate  5   b  from making elastic displacement relative to the upper base plate  5   a  in directions orthogonal to the yaw axis direction, and which join the upper base plate  5   a  and the lower base plate  5   b  elastically. This can simplify a calculation by a CPU concerning control of the walking of the walking robot. This can prevent disturbance, which would otherwise occur due to the friction resistance stemming from the physical interference by the rigid members. In addition, this can prevent the 6-axis force sensor from being broken, and can also prevent an equivalent to the breakage.

FIELD OF THE INVENTION

The present invention relates to an impact absorbing mechanism forimproving the stability of a compliance control which is used to controlthe posture of a walking robot.

BACKGROUND ART

Heretofore, there has been a problem that, during walk of a walkingrobot having a plurality of movable legs, a leg link mechanism orprecision apparatuses, such as sensors, included in the leg linkmechanism are apt to be broken due to a touch-down impact caused whenthe leg link mechanism and the external environment, including theground and a floor, collide with each other. In order to prevent thisproblem, some walking robots include, in the foot of the extremities ofthe movable legs of the robot, an impact absorbing mechanism forabsorbing the touch-down impact, for example, which uses rubber busheswith low rigidity and the like.

Some of those walking robots further include a 6-axis force sensor. Thissensor is used for control of walk by the walking robots having movablelegs, in particular, for compliance control of the foot joints withregard to control of bipedal walking. In the foot of the extremity ofeach of the movable legs, the sensor is installed between a lower baseplate and an upper base plate. The lower base plate has a surface tocontact the ground, a floor and the like, and is an equivalent to thefoot sole. The upper base plate is joined to the foot joint, andsupports the upper structure of the robot including the rest part of themovable leg.

Furthermore, with regard to a compliance control of the foot joints incontrol of walk of a bipedal walking robot, the 6-axis force sensormeasures a reaction force from the lower base plate, which is caused dueto a contact of the lower base plate mainly with the ground and thelike, as force components respectively in the yaw axis direction(perpendicular direction), the roll axis direction (antero-posteriordirection) and the pitch axis direction (left-right direction), as wellas moment components respectively about the axes. On the basis of theseparameters, a CPU (central processing unit) included in the main body ofthe robot performs calculations. Thereby, each of the joints in itsmovable legs is controlled.

At this point, with regard to the foot mechanism provided with elasticmembers, such as the rubber bushes, constituting the impact absorbingmechanism, the force components and the moments about the axes to bemeasured by the 6-axis force sensor have the respective deviations dueto elastic displacements of the elastic members respectively with regardto the yaw-axis, the roll-axis and the pitch-axis. When the walking ofthe robot is controlled, this complicates the calculation by the CPUincluded in the main body of the robot.

If the deviations of the force components in the respective axisdirections and the deviations of the moments about the respective axeswere kept constant, this can make it simple to control the walking ofthe robot. To this end, with regard to the elastic displacements in theelastic members which are interposed between the lower base plate andthe upper base plate in each of the foot mechanisms for the purpose ofimpact absorption, it is preferable that the respective rotationalspring constants concerning displacements relatively of the base platesbe kept constant, and that displacement to maintain the relativepositional relationship between the base plates be made isotropic.

More specifically, it is preferable that a walking robot be configuredto restrict displacements (deviations) in the axis directionsrespectively of the lower base plate and the upper base plate, which areinappropriate for controlling of the walking of the robot, by thefollowing measures. In order that elastic displacement with low rigiditydue to the impact absorbing mechanism including the rubber bushes andthe like may absorb a reaction force from the lower base plate and theload from the upper base plate, including the dead weight of the robot,first, elastic displacement with low rigidity concerning theperpendicular direction (yaw-axis direction) is allowed. Second,concurrently, the elastic displacement has a high rigidity concerningthe axis directions orthogonal to the perpendicular direction.

With regard to the walking robot having movable legs, however, when thelower base plate of each of the legs touches down to a slope, the groundin a rough terrain condition or the like, the elastic members, such asthe rubber bushes, constituting the impact absorbing mechanism causedisparate elastic displacements which respectively vary in displacementamount with regard to each of the axis directions. For this reason,rotational spring constants respectively of the elastic displacementscan not be constant. Accordingly, displacements for maintaining therelative positional relationships between the base plates are hinderedfrom being isotropic.

In addition, while the robot having movable legs is walking, inparticular while a bipedal walking robot is walking, when a free leg (aleg in motion, which is not in contact with the ground) is swungforward, this causes a torque about the yaw axis (a moment of rotation)in a supporting leg (a leg being in contact with the ground, andsupporting the load including the dead weight of the robot).Accordingly, a large spinning force acts about the yaw axis with thesupporting leg working as a center of rotation. This causes the elasticmembers, such as the rubber bushes, constituting the impact absorbingmechanism to respectively make elastic displacements due to thedistortion chiefly about the yaw axis. Concurrently, the elasticdisplacements respectively about the roll axis (the axis in theantero-posterior direction) and the pitch axis (the axis in theleft-right direction), both of which are orthogonal to the yaw axisdirection, become so disparate that their displacement amounts differfrom each other. As a result, the displacements for maintaining therelative positional relationship between the base plates cannot beisotropic. This complicates the control of the walking of the robot.

In order to restrict such disparate elastic displacements respectivelyof the elastic members, whose respective displacement amounts vary fromone to another, and in order to accordingly make isotropic the relativedisplacement between the upper base plate and the lower base plate whichis an equivalent to a foot sole, it has been essential that aconventional robot be provided with a guide mechanism using rigidmembers such as plates, which allow the elastic members to make therespective elastic displacements in the yaw axis direction, and whichhave high rigidity concerning the axis directions orthogonal to the yawaxis direction. This restricts displacements (deviations) in the axisdirections between the lower base plate and the upper base plate, whichare inappropriate for controlling of the walking of the robot (seeJapanese Patent Laid-open No. Hei.11-033941, Paragraph [0029], and FIG.1, for example).

However, if the guide mechanism using the rigid members in this mannerwere installed in the robot, this brings about the following problem.First, the installation increases the weight of the foot mechanism,accordingly increasing the inertial moment, which needs to be suppressedin each of the movable legs of the walking robot. In addition, thisinstallation causes each of the members with high rigidity and acorresponding elastic member to contact each other, accordingly causingfrictional resistance. As a result, this frictional resistance, asdisturbance, acts on the control of the walking of the robot.

Furthermore, the additional installation of the guide mechanism usingthe rigid members brings about another problem. The additionalinstallation complicates the foot mechanism. Depending on conditions ofthe walking posture of the robot, the rigid members interfere physicallywith the 6-axis force sensor in conjunction with displacement of theelastic members such as the rubber bushes. Accordingly, this breaks theforce sensor.

Moreover, with regard to the compliance control, while the 6-axis forcesensor measures a reaction force from the lower base plate to be causeddue to the lower base plate's contact chiefly with the ground and thelike, the impact absorbing mechanism, such as the rubber bushes, forabsorbing an impact caused due to the lower base plate's contact withthe ground and the like, absorbs the touch-down impact. For this reason,the impact absorbing mechanism is preferable in protecting the robot'sjoint structures including the sensor devices such as the 6-axis forcesensors, and the leg link mechanism. However, the elastic displacementswith low rigidity, which are properties of the impact absorbingmechanism, causes vibrations. Accordingly, the vibrations remain duringthe period of vibration damping. This inadequately vibrates the 6-axisforce sensor. As a consequence, the vibration acts, as disturbance, onthe control of the walking of the robot.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mechanism whichsolves the aforementioned problems advantageously. An impact absorbingmechanism for a walking robot according to the present invention is animpact absorbing mechanism provided to a foot of the extremity of eachof a plurality of movable legs of a walking robot having the movablelegs. The impact absorbing mechanism is characterized as including anupper base plate joined to a foot joint of each of the movable legs; alower base plate positioned below the upper base plate, and beingopposite to the upper base plate; and at least three elastic membersanisotropic in terms of elasticity, which are arranged at equalintervals in the circumferential direction about a predetermined axisline extending in the direction perpendicular to the upper base plate,between the upper base plate and the lower base plate, which allow thelower base plate to make elastic displacement relative to the upper baseplate in the same direction as the predetermined axis direction extends,while inhibiting the lower base plate from making elastic displacementrelative to the upper base plate in the directions orthogonal to thepredetermined axis direction, and which join the upper base plate andthe lower base plate elastically.

Such a configuration makes it possible to maintain deviations of therespective force components concerning the axis directions in the footand deviations of the respective moments about the axes. Specifically,the elastic members arranged between the upper base plate and the lowerbase plate which is an equivalent to the foot sole in the foot make itpossible to keep constant the respective rotational spring constantsconcerning relative displacement between the base plates. Concurrently,the elastic members make it possible to make isotropic displacement formaintaining the relative positional relationship between the baseplates. This enables a calculation by the CPU concerning the control ofthe walking of the robot to be simplified.

At this point, if only a rotation about the predetermined axis line (theyaw axis) extending in a direction perpendicular to the upper base plateis intended to be restricted, it suffices to arrange two elastic membersbetween the lower base plate and the upper base plate. In a case wherethe number of elastic members is two, however, the elastic members cannot restrict a rotation about one of the two axis lines (the roll axisand the pitch axis), each of which is orthogonal to the predeterminedaxis line (the yaw axis), and which are orthogonal to each other. Bycontrast, according to the present invention, at least three elasticmembers are arranged at equal intervals in the circumferential directionabout the predetermined axis line (the yaw axis). These elastic memberscan allow the lower base plate to make elastic displacement relative tothe upper base plate in the same direction as the predetermined axisline (the yaw axis) extends. Concurrently, these elastic members canrestrict a rotation of the lower base plate relative to the upper baseplate about the axis lines orthogonal to the predetermined axis line(the yaw axis), with regard to the two axis lines (the roll axis and thepitch axis), each of which is orthogonal to the predetermined axis line(the yaw axis), and which are orthogonal to each other, in a equalmanner.

In addition, the impact absorbing mechanism according to the presentinvention does not use the guide mechanism employing rigid members, suchas plates, which have been essential for the conventional impactabsorbing mechanism between the lower base plate and the upper baseplate in each of the feet. The impact absorbing mechanism according tothe present invention can be configured to have only elastic members,instead. Accordingly, the very simple configuration can realize theimpact absorbing mechanism which is preferable in controlling thewalking of the robot. This can prevent disturbance which would otherwiseoccur due to the friction resistance stemming from the physicalinterference by the rigid members. In addition, this can prevent the6-axis force sensor from being broken.

Furthermore, the impact absorbing mechanism does not require the guidemechanism using the rigid members. This decreases the weight of each ofthe feet, thus enabling the inertial moment acting on the forward swingof each of the movable leg to be reduced. Accordingly, this reductionenables load imposed on each of the joints of the movable leg to bedecreased. This makes it possible to improve a speed at which the robotwalks, and also makes it possible for the robot to do such as maintain,and recover, the posture promptly.

It should be noted that the impact absorbing mechanism of a walkingrobot according to the present invention may include at least three highdamping members which are arranged at equal intervals in thecircumferential direction about the predetermined axis line, between theupper base plate and the lower base plate, and which damp the vibrationof the lower base plate relative to the upper base plate. This inclusioncan damp the vibration to be caused due to the impact absorbingmechanism in each of the feet effectively and in a short period of time.This makes it possible to inhibit the vibration inadequate for thecontrol of the walking of the robot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of an impactabsorbing mechanism of a walking robot according to the presentinvention, in a state of being seen through, along with other parts ofthe robot.

FIG. 2 is an exploded, perspective view showing a foot including theimpact absorbing mechanism according to the embodiment, along with ashank of a movable leg and a foot joint of the robot.

FIGS. 3 a and 3 b are respectively a plane view and a side view showingthe impact absorbing mechanism according to the present invention.

FIG. 4 is a cross-sectional view taken along the A-A line in FIG. 3 b.

FIG. 5 is a cross-sectional view taken along the B-B line in FIG. 3 a.

FIG. 6 is a cross-sectional view taken along the C-C line in FIG. 3 a.

FIG. 7 is an explanatory diagram showing an operational condition of theimpact absorbing mechanism according to the present embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, descriptions will be provided for an embodiment of thepresent invention, by use of an example, on the basis of the drawings.FIG. 1 is a perspective view showing an embodiment of an impactabsorbing mechanism of a walking robot according to the presentinvention, in a state of being seen through, along with the other partsof the robot. FIG. 2 is an exploded, perspective view showing a footincluding the impact absorbing mechanism according to the embodiment,along with a shank of a movable leg and a foot joint of the robot. FIGS.3 a and 3 b are respectively a plane view and a side view showing theimpact absorbing mechanism according to the present invention. FIG. 4 isa cross-sectional view taken along the A-A line in FIG. 3 b. FIG. 5 is across-sectional view taken along the B-B line in FIG. 3 a. FIG. 6 is across-sectional view taken along the C-C line in FIG. 3 a. FIG. 7 is anexplanatory diagram showing an operational condition of the impactabsorbing mechanism according to the present embodiment.

In the figures, reference numeral 1 denotes a bipedal walking robot; 2,movable legs of the robot; 3, shanks respectively of the movable legs 2;4, foot joints provided respectively to the extremities (lower ends) ofthe shanks; 5, feet which are joined respectively to the foot joints 4,and which are rotated relative to the shanks 3 respectively about theyaw axis YA, the roll axis RA and the pitch axis PA in conjunction withoperations of the respective foot joints 4; and 4 a to 4 c, covers foreach of the foot joints 4. At this point, each of feet 5 includes: anupper base plate 5 a joined to the foot joint 4; a lower base plate 5 bwhich is arranged below the upper plate 5 a, and which is opposite tothe upper plate 5 a; an upper cover 5 c; and a lower cover 5 d. The yawaxis YA passes through the center of the upper base plate 5 a, andextends perpendicularly to the upper base plate 5 a. The roll axis RAand the pitch axis PA are orthogonal to the yaw axis YA, and extendrespectively in the antero-posterior direction and the left-rightdirection of each of the movable legs 2.

The impact absorbing mechanism according to the present embodiment,which is provided to such feet 5, includes three elastic members 6anisotropic in terms of elasticity (for example, “Ultra Bush” which isthe name of the product made by NOK Corporation) as follows, in additionto the upper base plate 5 a and the lower base plate 5 b. The elasticmembers 6 are arranged, about the yaw axis YA extending in a directionperpendicular to the upper base plate 5 a, at equal intervals which keepeach neighboring two of the three elastic members 6 separate from eachother by an angle of 120° in the circumferential direction. Each of thethree elastic members 6 allows the lower base plate 5 b to make elasticdisplacement relative to the upper base plate 5 a in the same directionas the yaw axis YA extends. On the other hand, each of the three elasticmembers 6 inhibits the lower base plate 5 b from making elasticdisplacement relative to the upper base plate 5 a in the same directionsas the roll axis RA and the pitch axis PA extend, which are orthogonalto the yaw axis YA. In addition, each of the three elastic members 6elastically joins the upper base plate 5 a and the lower base plate 5 btogether.

As shown in FIG. 5, each of the three elastic members 6 includes anouter cylinder 6 a, an inner cylinder 6 b, and a rubber-like elasticbody 6 c which is interposed between the outer cylinder 6 a and theinner cylinder 6 b, and which are adhered to the outer cylinder 6 a andthe inner cylinder 6 b by vulcanization. Each of the three elasticmembers becomes similar to a rubber mount. It is rigid in the radiusdirection, and is soft in the axis direction and the torsionaldirection. At this point, the outer cylinder 6 a is fitted into, andfixed to, the lower base plate 5 b. The inner cylinder 6 b is fixed tothe upper base plate 5 a with a bolt.

In addition, as shown in FIG. 6, the impact absorbing mechanismaccording to the present embodiment includes three high damping members7 as follows (for embodiment, “High Damping Rubber” which is the name ofthe product made by NOK Corporation). The three high damping members 7are arranged about the yaw axis YA at equal intervals which keep eachneighboring two of the three high damping members 7 separate from eachother by an angle of 120° in the circumferential direction, between theupper base plate 5 a and the lower base plate 5 b. The three highdamping members 7 are respectively adjacent to the three elastic members6. The three high damping members 7 damp vibration of the lower baseplate 5 b relative to the upper base plate 5 a. Each of the three highdamping members 7 includes: a disc-shaped seat plate 7 a whose screwshank protrudes downwards; and a rubber-like elastic body 7 b, shapedlike a cylinder, which is adhered to the upper surface of the seat plate7 a by vulcanization. The rubber-like elastic body 7 b of each of thehigh damping members 7 has a lower degree of elasticity and a higherdegree of viscoelasticity than the rubber-like elastic body 6 c of eachof the elastic members 6. In this case, the seat plate 7 a is screwedto, and fixed to, the lower base plate 5 b. The rubber-like elastic body7 b is fixed to the upper base plate 5 a with a bolt.

The impact absorbing mechanism according to the present embodiment cankeep constant deviations respectively of force components in the samedirections as the yaw axis YA, the roll axis RA and the pitch axis PAextend, as well as constant deviations respectively of moments about theaxes, with regard to each of the feet 5. Specifically, the elasticmembers 6 arranged between the upper base plate 5 a and the lower baseplate 5 b which is an equivalent to the foot sole in each of the feet 5make it possible to keep constant the respective rotation springconstants concerning relative displacement between the base plates 5 aand 5 b. Concurrently, the elastic members 6 can make it possible tomake isotropic displacement for maintaining the relative positionalrelationship between the base plates 5 a and 5 b. This can simplify acalculation by the CPU concerning the control of the walking of therobot.

In other words, according to the present embodiment, the three elasticmembers 6 are arranged at equal intervals in the circumferentialdirection about the yaw axis YA. Accordingly, the impact absorbingmechanism according to the present embodiment can allow the lower baseplate 5 b to make elastic displacement relative to the upper base plate5 a in the same direction as the yaw axis YA extends. Concurrently, theimpact absorbing mechanism can restrict a rotation of the lower baseplate 5 b relative to the upper base plate 5 a about the axis linesorthogonal to the yaw axis YA, with regard to the roll axis RA and thepitch axis PA, each of which is orthogonal to the yaw axis YA, and whichare orthogonal to each other, in an equal manner.

In addition, the impact absorbing mechanism according to the presentembodiment does not use the guide mechanism employing rigid members,such as plates, which have been essential for the conventional impactabsorbing mechanism between the lower base plate and the upper baseplate in each of the feet. Accordingly, the impact absorbing mechanismcan be configured to have only elastic members 6 and high dampingmembers 7, instead. This very simple configuration can realize theimpact absorbing mechanism which is preferable in controlling the walkof the robot. This can prevent disturbance, which would otherwise occurdue to the friction resistance stemming from the physical interferenceby the rigid members. In addition, this can prevent the 6-axis forcesensor from being broken, and can also prevent an equivalent to thebreakage.

Furthermore, the impact absorbing mechanism according to the presentembodiment does not require the guide mechanism using the rigid members.This decreases the weight of each of the feet 5, thus enabling aninertial moment acting on the forward swing of each of the movable legs2 to be reduced. Accordingly, this reduction enables load imposed on thejoints of each of the movable legs 2 to be decreased. This makes itpossible to improve a speed at which the walking robot 1 walks, and alsomakes it possible for the robot 1 to do such as maintain, and recover,the posture promptly.

Additionally, the impact absorbing mechanism according to the presentembodiment includes the three high damping members 7, which are arrangedat equal intervals in the circumferential direction about the yaw axisYA, between the upper base plate 5 a and the lower base plate 5 b, andwhich damp the vibration of the lower base plate 5 b relative to theupper base plate 5 a. This inclusion can decrease the vibration to becaused due to the impact absorbing mechanism in each of the feet 5effectively and in a short period of time. This makes it possible toinhibit the vibration inadequate for the control of the walking of therobot.

Hereinbefore, the impact absorbing mechanism has been described on thebasis of the illustrated embodiment. However, the present inventionshould not be limited to the aforementioned embodiment. Theconfiguration and the number of the elastic members 6 and the highdamping members 7, for embodiment, can be changed within the scope andthe spirit of the descriptions of the claims.

INDUSTRIAL APPLICABILITY

The impact absorbing mechanism for a walking robot according to thepresent invention can keep constant the deviations respectively of theforce components in the axis directions, and the deviations respectivelyof moments about the axes, with regard to each of the feet. This cansimplify the calculation by the CPU concerning control of the walking ofthe walking robot. In addition, the very simple configuration canrealize the impact absorbing mechanism which is preferable incontrolling the walk of the robot. This can prevent disturbance, whichwould otherwise occur due to the friction resistance stemming from thephysical interference by the rigid members. In addition, this canprevent the 6-axis force sensor from being broken, and can also preventan equivalent to the breakage. Furthermore, the load imposed on thejoints of each of the movable legs can be decreased. This makes itpossible to improve a speed at which the walking robot walks, and alsomakes it possible for the robot to do such as maintain, and recover, theposture promptly.

1. An impact absorbing mechanism for a walking robot, the impactabsorbing mechanism provided to a foot of an extremity of each of aplurality of movable legs of the walking robot having the movable legs,comprising: an upper base plate joined to a foot joint of each of themovable legs; a lower base plate positioned below the upper base plate,and being opposite to the upper base plate; and at least three elasticmembers anisotropic in terms of elasticity, which are arranged at equalintervals in a circumferential direction about a predetermined axis lineextending in a direction perpendicular to the upper base plate, betweenthe upper base plate and the lower base plate, each of which allows thelower base plate to make elastic displacement relative to the upper baseplate in the same direction as the predetermined axis direction extends,while each of which inhibits the lower base plate from making elasticdisplacement relative to the upper base plate in directions orthogonalto the predetermined axis direction, and which join the upper base plateand the lower base plate elastically.
 2. The impact absorbing mechanismfor a walking robot according to claim 1, comprising: at least threehigh damping members which are arranged at equal intervals in acircumferential direction about the predetermined axis line, between theupper base plate and the lower base plate, and which damp vibration ofthe lower base plate relative to the upper base plate.